1. Field of the Invention
The present invention relates to a thin invert composition for carrying agricultural products to a target area, such as a field of growing crops, in the form of a spray of uniform small droplets. More specifically, the invention relates to low viscosity water and oil emulsions for carrying hydrophilic agricultural products such as herbicides, insecticides, fungicides and/or plant growth regulators.
2. Prior Art
Oil/water emulsions are known per se, and have been used for agricultural applications as a means to form larger droplets when the emulsion is sprayed, as compared for example to a dispersion of the agricultural product in water. A larger droplet has more inertia than a smaller one, and is less apt to drift. Drift is a problem, particularly in aerial application of the agricultural product, allowing a portion of the product to escape due to air currents carrying the product away from the target area, evaporation, etc. At worst the drifting product can pollute the environment, for example adversely affecting areas surrounding the area of intended application. At the least a portion of the product fails to reach the target crop or the like and is wasted.
A number of factors affect droplet size including the viscosity of the composition, its surface tension, the geometry and flow conditions of the spray apparatus which emits the composition, and the relative motion of the air stream into which the spray is emitted. These factors are interrelated. For example, a composition with a relatively high surface tension may be capable of forming a large droplet under optimal conditions, but under typical spray conditions the viscosity, spray geometry and/or flow conditions are so variable that the spray is broken up into a range of droplet sizes. The larger droplets tend to fall and the smaller droplets tend to drift. It is difficult to prevent the breakup of larger droplets into smaller ones, particularly considering the fact that the high viscosity of the composition needed to produce a large droplet size requires a large diameter flow path and spray orifice in order to flow properly. Moreover, viscosity varies with temperature, minor variations in water quality, agitation, etc.
The efficacy of the agricultural agent in the composition is affected by the droplet size. The general objectives when spraying are to coat the target area evenly and completely, and to apply the composition in a quantity per unit of area that will achieve the desired results. However, when the droplet size is large or variable these factors are also variable. With respect to leafy vegetation, for example, large droplets applied at a given quantity per unit area are more likely to spot the leaves than to coat them evenly. Therefore, large droplets may be helpful against drift but require a higher rate of application to achieve a given efficacy.
Some active agricultural products can be dispersed in either water or oil. However, many forms of vegetation have a more or less waxy surface which protects the plant from dehydration due to evaporation from the leaves. This waxy coating also interferes with the absorption of water into the leaves. Accordingly, spray compositions with water soluble agricultural products are often considered less advantageous than oil based compositions because the active ingredient can be blocked from penetrating the leaves due to the waxy coating.
Known oil/water emulsions, particularly when applied by aerial spraying, have additional drawbacks. When ambient temperatures rise, the more volatile media tend to evaporate from the emulsion more quickly, and may release the active agricultural product into the air rather than onto the target. When a droplet containing a mixture of a water soluble active ingredient, water and oil is sprayed, at least some of the water on the surface of the droplet tends to evaporate or separate from the droplet, thereby wasting the agricultural product and impeding drift control. Under such circumstances, the droplets (primarily remaining oil) are reduced in size and can float more readily in the air and be carried from the target by the wind.
As mentioned above, the droplet size of a sprayed composition can be increased by using a thick so-called "invert." An invert is an emulsion characterized by droplets having a film of oil surrounding one or more water particles, and thick inverts are viscous compositions of this type. The oil phase surrounding the water phase reduces the evaporation of the water and consequent loss of the active ingredient. However, thick invert emulsions form non-uniform droplets when sprayed. Due to the large and non-uniform character of the droplets, thick inverts require higher spray volumes per unit of area to achieve a given efficacy than might be obtained with smaller droplets of a uniform size, which can more evenly coat the leaves A typical thick invert may require application rates of 25 to 100 gallons per acre.
A known, boom-type aerial agricultural spray device is disclosed in U.S. Pat. No. 5,110,048 which is hereby incorporated. A plurality of orifices are provided on the trailing edge of an airfoil shaped conduit which is elongated transverse to the direction of travel of an aircraft, for example on the front of the skids of a helicopter or below the wing of a fixed-wing aircraft. The orifices are arranged on nozzles which are wedge-shaped along their trailing edge, each having a valve coupled to a port which protrudes at a fitting on the leading edge of the airfoil.
A conventional delivery system is characterized by substantial disturbance of the laminar flow of air passing the aircraft or the like. The disturbance and eddies interfere with formation of uniform droplets. This is particularly true when a conventional boom is used with fixed-wing aircraft (where turbulence generated by the wing further disturbs the laminar flow around the spray boom). The conventional device emits the liquid in a distribution of larger and smaller droplets. Droplets larger than optimum require high application rates. Droplets smaller than optimum tend to drift. In all, the known device is largely subject to drift and waste.
Assuming that a uniform application of small droplets can be accomplished, the volume of material applied to a site to be treated can be reduced. With more accurate application, a more concentrated agent can be applied safely. Smaller, lighter equipment can be used to apply the material, and the effectiveness of the agent is improved. Moreover, when the small droplets can be formed as an invert with a water phase enclosed in an oil surface layer, problems with evaporation are reduced. Moreover, the oil assists in penetration of the waxy surface of vegetation, and the overall efficacy of the chemical agent is improved.
According to the invention, a composition is provided which can be readily applied through small orifice spraying devices arranged to form uniform small droplets. The orifices are capillary sized in relation to the composition viscosity and surface tension. The composition is low in viscosity and is agitated to maintain the oil and water against separation or to reconstitute the emulsion after separation. This is accomplished, for example, by recirculating the composition in the spray apparatus, using the spray pump or an auxiliary pump associated with the spray apparatus. The agitation converts the oil and water phases into a thin invert which produces a droplet having an oil phase over a water phase, the oil phase providing protection against evaporation of the water phase, and producing surface tension characteristics needed to maintain droplet size.
Together with a novel spray apparatus as disclosed in a commonly owned and concurrently filed application entitled Delivery Apparatus for Thin Invert Emulsions, the composition of the invention produces uniform small droplets that provide excellent efficacy in low volume application. The viscosity of the composition is low, as appropriate for emission through numerous small orifices to form small droplets. The viscosity of the composition can also be controlled by regulating the extent of agitation. Therefore, problems with separation of the oil and water portions of the formulation are overcome, allowing an invert solution to be applied in uniform small droplets. In connection with aerial spraying, a plurality of wedge shaped nozzles along an aerodynamically shaped conduit are each provided with trailing small tubes leading to an internal manifold coupled to the conduit at a check valve. A pump coupled between a storage reservoir and an end of the conduit pressurizes the conduit to open the check valves and commence application of the product. A second conduit runs along the conduit and is preferably disposed inside the conduit. The second conduit is arranged in a recirculation path adapted to agitate the material in the system to prevent separation and to regulate the viscosity of the composition, which varies with agitation, temperature and ingredients.